This invention relates to a method for activating preformed, crystalline aluminum phosphates by combining these aluminum phosphates with an activating metal oxide, such as silica, and water under conditions sufficient to increase the acid catalytic activity of the material.
Aluminum phosphates are taught in U.S. Pat. Nos. 4,310,440 and 4,385,994, for example. Aluminum phosphate materials have electroneutral lattices and, therefore, are not useful as ion-exchangers or as catalyst components. Microporous aluminum phosphates have a composition typified as: EQU xR : Al.sub.2 O.sub.3 : (1.0.+-.0.2) P.sub.2 O.sub.5 : yH.sub.2 O
wherein R is an organic amine or quaternary ammonium salt entrapped within the aluminum phosphate and playing a role as crystallization template, x and y representing the amounts of R and H.sub.2 O needed to fill the microporous voids. Because of the aluminum/phosphorus atomic ratio of these materials is about unity, they display virtually no ion-exchange properties, the framework positive charge on phosphorus being balanced by corresponding negative charge on aluminum: EQU AlPO.sub.4 =(AlO.sub.2.sup.-)(PO.sub.2.sup.+)
The phosphorus-substituted zeolites of Canadian Pat. Nos. 911,416; 911,417 and 911,418 are referred to as "aluminosilicophosphate" zeolites. Some of the phosphorus therein appears to be occluded, not structural. These latter materials containing silicon, aluminum and phosphorus are characterized by the general formula: EQU M.sub.(x-y) :x(AlO.sub.2.sup.-):(SiO.sub.2):y(PO.sub.2.sup.+):zH.sub.2 O
wherein M is a monovalent cation, x is approximately 1-4, y is 0.05-1.0 and z is the number of hydration water molecules. Structural replacement of silicon with phosphorus has been realized in materials called silica clathrates (West German Patent No. 3,128,988).
U.S. Pat. No. 4,363,748 describes a combination of silica and aluminum-calcium-cerium phosphate as a low acid activity catalyst for oxidative dehydrogenation. Great Britain Patent No. 2,068,253 discloses a combination of silica and aluminum-calcium-tungsten phosphate as a low acid activity catalyst for oxidative dehydrogenation. U.S. Pat. No. 3,801,704 teaches an aluminum phosphate treated in a certain way to impart acidity. U.S. Pat. No. 4,228,036 teaches an alumina-aluminum phosphate-silica matrix as an amorphous body to be mixed with zeolite for use as cracking catalyst. U.S. Pat. No. 3,213,035 teaches improving hardness of aluminosilicate catalysts by treatment with phosphoric acid. The catalysts are amorphous.
U.S. Pat. No. 2,876,266 describes an active silicophosphoric acid or salt phase of an amorphous material prepared by absorption of phosphoric acid by premolded silicates or aluminosilicates.
Other teachings of aluminum phosphates and their preparation include U.S. Pat. Nos. 4,365,095; 4,361,705; 4,222,896; 4,210,560; 4,179,358; 4,158,621; 4,071,471; 4,014,945; 3,904,550 and 3,697,550. Since their neutral framework structure is void of ion-exchange properties, they are used as catalyst supports or matrices.
The crystalline silicophosphoaluminates synthesized in accordance with the aforementioned U.S. application Ser. No. 562,673 are molecular sieve or other framework structures exhibiting ion-exchange properties and are easily and conveniently converted to materials having intrinsic catalytic activity. Techniques for synthesis of zeolites or aluminum phosphates taught in the art are not useful for synthesis of these crystalline silicophosphoaluminates.